The invention relates to a cylinder head bolted connection of an internal combustion engine.
Cylinder head bolts, especially of internal combustion engines made of lightweight metal, are subjected to high stresses, for example, after a cold start. These stresses result from the differences in thermal expansion between the housing parts of the internal combustion engine on the one hand and the cylinder head bolts on the other. While the components such as the cylinder head and adjoining areas of the cylinder block which are made of an aluminum alloy for example and are heated relatively rapidly by the combustion process in the combustion chamber, expand by comparatively large amounts, the cylinder head bolts which are made of a steel alloy and are insulted by an air gap along nearly their entire length remain at a low temperature level for a relatively long time and are subject to less expansion; consequently, during a certain time interval, there is a sharp increase in the bolt forces transmitted by the cylinder head bolts. This can lead to undesired flow of the material in the contact surfaces of the cylinder head for the heads of the cylinder head bolts.
The bolt force increase also occurs to a varying extent in the cylinder head bolts of an internal combustion engine so that unequal expansions and consequently unequal pressures can be exerted on the cylinder head gasket located between the cylinder head and the cylinder block. Consequently, this gasket in unfavorable cases can burn pointwise, in turn leading to total failure of the internal combustion engine. These problems occur to a greater degree in air cooled internal combustion engines.
German Patent Document DE 39 39 230 A1 teaches filling holes for cylinder head bolts designed as tie rods with a permanently plastic material after the bolts are inserted, to avoid corrosion, for oil-tight separation, and to avoid bolt vibrations.
An object of the invention is to reduce the undesired increase in the bolt forces transmitted by the cylinder head bolts of an internal combustion engine to the greatest degree possible.
This object is achieved according to preferred embodiments of the invention by providing heat-conducting material in the annular gap between the bolt shaft and wall sections of the engine.
When a heat-conducting material is located in an internal combustion engine in the space, in the form of an annular gap, necessarily left between the shaft of a cylinder head bolt and the adjacent housing walls, said material being in positive contact both with the shaft and the housing walls in the system, the clearly improved heat flux relative to that obtained with an air gap produces a comparatively small time delay between the increasing heating of the housing parts and the cylinder head bolts. Consequently, the cylinder head bolts expand more rapidly than the housing parts, so the difference in expansion is less and the bolt force increase is markedly reduced.
Flow of the material in the vicinity of the bold head support is retarded and uniform expansion of cylinder head bolts of a cylinder for example is reduced to a degree that does not have an adverse effect on the cylinder head gasket.
Advantageously, existing cylinder head bolts can be operated with significantly higher safety reserves or they can be optimized in a manner that reduces both cost and weight with regard to their geometric dimensions and their material quality.
In one advantageous embodiment of the invention, a wire knit, a fine-grained metal powder, or an aluminum bushing can be used as the material placed in the annular gap.
A wire knit can be used economically as a commercial component, since because of its axial and radial crushability, it can be inserted into the annular gap in such fashion that, after the cylinder head has been bolted down, it presses against the adjacent components under radial pressure, ensuring good heat transfer.
A fine-grained metal powder according to another preferred embodiment of the invention largely expels the air in the annular gap and forms a comparatively large surface for heat transfer. As a result of the locally high temperature, by a suitable choice of the metal powder, welding of the grains can be promoted which improves heat flux because of the resultant metallic bridges. Trouble-free disassembly of the cylinder head bolts is also ensured.
A comparatively soft aluminum bushing according to another preferred embodiment of the invention is crushed within certain limits when the cylinder head bolt is screwed into the annular gap and thereby offers a heat flux with positive contact over a large area.
Alternatively, the annular gap can be filled with a liquid, preferably oil, with additional measures being required for sealing according to another preferred embodiment of the invention. If the annular gap extends at least partially into all of the components involved in the cylinder head bolted connection, the heat flux can be made uniform so that all area of the bolt shaft are heated largely uniformly.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.